1. Field of the Invention
The present invention relates to a method for synthesis of secondary alcohols, particularly to a method for synthesis of secondary alcohols by addition of organoboronic acids with aldehydes in presence of the cobalt ion and bidentate ligands.
2. Description of the Prior Art
Chiral secondary alcohols are key structural units present in various biologically and pharmaceutically active compounds. Transition-metal-catalyzed addition of organometallic reagents with aldehydes is a key method for the synthesis of substituted secondary alcohols. Among them, organoboronic reagents have gained much attention due to the advantages of air and moisture stability, low toxicity, and availability. Among the transition-metal-catalysts, rhodium, palladium, platinum and nickel complexes efficiently catalyzed the addition reaction of organoboronic acids with aldehydes. Recently, copper- and iron-catalyzed addition reactions of organoboronic acid with aldehydes were also reported. However, the scope of aldehydes in these addition reactions is rather limited. Only aromatic aldehydes with an electron-withdrawing substituent worked well. Despite the fact that various metal-catalyzed addition reactions of organoboronic acids with aldehydes are available in the literature, only a few reports on asymmetric reactions were discussed.
Zhou et al. (Org. Lett. 2006, 8, 1479) reported a rhodium-catalyzed enantioselective addition reaction of aromatic boronic acids with aromatic aldehydes. In the reaction, enantiomeric excess (ee) values of 62-87% for chiral biaryl methanols were observed.
Recently, Miyaura et al (Angew. Chem. Int. Ed. 2009, 48, 4414) reported a ruthenium-catalyzed enantioselective addition reaction of aromatic boronic acids with aromatic aldehydes. In the reaction, the expected chiral biaryl methanols were observed in excellent enantiomeric excess. However, in these reactions specially designed chiral ligands and expensive ruthenium or rhodium catalysts were used.
To sum up, the development of new, mild and convenient methods using a low-cost catalyst for the synthesis of chiral secondary alcohols remains highly attractive.